This invention relates to illumination systems, and more particularly relates to a two-source illumination system having a high light output.
Light emitted from illumination systems can be modulated by an array of picture elements or pixels whose transmittance or reflectance can be changed in response to an electrical signal, thus creating a display. The modulating array is sometimes referred to as a light valve.
In light valve projection systems, such as those employing LCD panels as light valves, the typical acceptance angle needed to provide an adequate level of display contrast is on the order of plus or minus 15 degrees. In projection systems which are proposed to employ DMD (deformable micromirrored device) panels as light valves, the acceptance angle is even narrower, for example, on the order of plus or minus 10 degrees. Collecting a high percentage of light from a light source over such a restricted collection angle has proven to be difficult in practice.
Light sources which have the combination of small arcs (on the order of 1 to 2 mm in length), high values of luminous efficacy and/or the ability to be driven at high power levels would seem to be the best suited for these demanding applications. However, only two known types of lamps come close to meeting these requirements; a 500 watt xenon arc lamp and a 100 watt high pressure discharge lamp. Both lamps have a small arc of about 1 mm. However, the xenon lamp has a relatively poor luminous efficacy of around 25 lumens per watt, while the high pressure lamp, although it has a somewhat higher luminous efficacy of about 60 lumens per watt, still cannon provide sufficient output to achieve the required brightness levels in the current projection systems employing DMD light valves.